Technical How to Identify a posi in a 9”

Hey all I’m looking to sell this 9” center section and the question is if it is posi or open. Is there anyway to tell from these photos? Thanks in advance all

 

Stick your finger in the ring gear side and feel for a gap in the splines. If there is a break in the splines it a posi. The break in the splines you are feeling, the inner, the spider gear, the outer is the clutch pack hub. If no break in the splines it's a open rear.
Just looking at it, I will guess its not a posi.

 

That is an open diff !!
Posi's have recessed crown wheel bolts


Open have crown wheel bolts that are flush on the surface

 

FWIW, "Crown wheel" is Kiwi speak for "ring gear".

 

^^^^^ May as well be called a… as well.

 

1640’s name (crown wheel) given in watch making.

 

I seem to remember (very dicey concept) that when I ever turned the input shaft on an open differential, the wheels would turn opposite directions. And if it was limited slip they would both turn the same direction.
Yes? No?

 

You’ll also want to know the gear ratio and the spline count for the axles, should be either 28 or 31.

 

TECH TIP:
A couple of splined stub ends from 28- and a 31-spline axles with a socket welded to the ends makes it easy for me to insert them into a pig and determine if if is 28-spline or 31-spline and whether it is posi, depending on if one shaft will easily rotate when the other is held still.

I also use them in a vice to determine the slippage torque (as specified in the shop manual) needed to be exerted on the clutches when rebuilding the posi units.

 

90 % of the 9 inch posi's I have taken out looked like that picture on the top. I think the ones in the Lincoln had a little more material in that area.

 

Everybody loves the 9" Ford, but most of them stock had really weak parts in them. And not a lot opted for Trac Loc.

 

Aweosme thank you

 

It’s a 31 spline thank you

 

I’d actually meant when you list it for sale. The gear ratio could also be attractive to someone.

 

Yep, when you list a center section describe what it is (gear ratio, posi/open, and spline count).

That's one of my pet peeves, especially when it comes to people selling wheels and not listing the width and backspacing or offset, and sometimes even the diameter.

 

Also bolt circle and stud count.

 

You're right, I forgot to mention that.

 

Oh yes, for sure it’s listed with ratio and spline count . Those I could figure out haha, the posi part had me a little lost at first

 

Yep I agree, had that part figured out.. the posi/open had me confused

 

Not an easy one to identify, spoken for GM guys like myself.

 

True. My grandfather was a watchmaker. Went to the Bradley Horology Institute to learn the trade.

 

That’s not a trac loc!



Bones